Class D

You would be hard pressed to find a ferrite core in a mid/tweeter for even a mid range speaker. Air core inductors are fairly cheap at the frequencies needed.  For woofers, there are trade-offs w.r.t. resistance / core impacts.


In speakers, the cross-over is in the audio band. In a Class-D amplifier it is not.  In a speaker you don't normally have steel nearby. In a Class-D amplifier you may.

Ferrite messes up the sound. So, why do we have ferrite coils on the output of all class D amps? It is because they are smaller, cost less, have less resistance, run cooler and have better contained fields so there would be less rf outputting the amp. It is not because they sound good. If you use a better sounding air core coil the board has to be bigger, the coil costs more, you have to use a large gauge coil to get the resistance down, and you might have to add more shielding in the amp to make it pass rf standards.

You got that right at least!! and it’s why ML in their megabuck class-D flop, use big "air cores" in their No.53 monoblock, and used 4 of them in series to get a far steeper slope to cut the switching frequency noise out, so it doesn’t affect the audio band phase integrity.
https://www.stereophile.com/images/styles/600_wide/public/011212ML53-600.jpg

Because the filter is set at 50K does not mean it does not effect the sound.  It's intrinsic sound is still there.  No free lunch.  Everything makes a difference.  But you have to listen to know.  Years ago I worked for an audiophile company that made tube stuff.  They had a zobel network on the output of one of their amps that had a .1 microfarad cap. .  I told them to change their junk mylar cap to a polystyrene but the owner said it was operating at high frequencies out of the audio band so it should not matter.  He humored me and tried it.  Of course, it sounded much better.  There are people that sell external zobel networks and the best sounding ones use the most expensive parts.  Again, no free lunch.....everything makes a difference.

Trouble is the Levinson sounded like crap.  Everything makes a difference....again....the truth is in the listening.  It does not matter that Levinson used a bunch of air core coils (one thing does not make a whole).......what matters is the sound.  They did not get it right. My modded Purifi uses ONE super sounding air core coil.  

Class D is just a cheap form of amplification. Another way to cut cost and corners. I read more than a few interviews from the high-end companies,and they all say "Stay away. The technology is not proven."
Especially when the products are from companies who’ve been around for 3 years,or that I’ve never heard in the first place.
Class A & Class A/B have been around forever with good reason.